A.F. Hall

The effect of saliva on enamel and dentine erosion

The present study aims to assess the ability of saliva, both in vitro and in situ, to prevent surface mineral loss from enamel and dentine when exposed to an erosive challenge. Fifteen groups of four varnished thin tooth sections were stored in saliva collected from individuals taking part in the in situ study and a further eight groups, each containing four sections, were stored in deionised water. In vitro, sections were stored in saliva or water for 14 days. In addition, fifteen subjects each wore an appliance with four varnished sections. Appliances with sections were worn for 14 days. All sections were exposed to 25 ml of erosion solution for 5 min twice daily. Microradiography and image analysis of the recovered sections demonstrated significant protection of surface mineral loss from enamel and dentine by saliva in vitro and in situ compared with deionised water (p < 0.05). Significantly less mineral loss (p < 0.05) was observed for enamel and dentine stored in situ compared with storage in saliva in vitro. Generalised linear modelling demonstrated both the subject and protocol had significant effect on mineral loss. A weak positive correlation (r = 0.64) was noted when in situ and in vitro mineral loss from enamel were compared, demonstrating greater reactivity of the in vitro enamel specimens to the erosion challenge. The dentine data did not show any linear correlation. Saliva protected against mineral loss by erosion and, for enamel, in vitro results demonstrated a weak positive correlation with in situ results.

Evaluation of enamel dental restoration interface by optical coherence tomography

Evaluation of molar dental restorations on enamel is performed using optical coherence tomography (OCT) with 10 microm resolution. Images of approximately 50 microm failure gaps in the restorations are demonstrated and the OCT images are compared with x-ray and optical microscopy pictures. The results demonstrate the potential of the technique for clinical evaluation of dental restorations.

In Vitro Studies of Laser Fluorescence for Detection and Quantification of Mineral Loss From Dental Caries

Laser fluorescence (LF) is thought to be a quantitative technique for the measurement of mineral loss from dental caries. These studies aimed to demonstrate the quantitative nature of LF, by means of transverse microradiography (TMR), in addition to the possible use of LF on small specimens suitable for in situ studies. Studies also aimed to determine the ability of LF to detect caries adjacent to amalgam restorations. The results demonstrated reasonable correlation between both the histological depth and mineral loss measured by TMR compared with the % change in mean fluorescence radiance measured by LF (r = 0.70 and 0.83, respectively). Studies with small specimens demonstrated that in vitro remineralization could be observed with LF for comparison of the demineralized specimen with an undemineralized reference. ANOVA showed significant mineral gain (p < 0.0001). The detection and quantification of mineral loss adjacent to amalgam restorations may have potential for the management of recurrent caries. Studies have demonstrated that LF can detect such mineral loss, and, with refinement of the image analysis system, LF was capable of detecting remineralization. Remineralization of such lesions is controversial, but it is suggested that LF may have a role in secondary caries management.

A clinical study of pulsed Nd: YAG laser-induced pulpal analgesia.

The pulsed Nd: YAG laser is advocated as an alternative means of providing analgesia during routine dental procedures. Since the evidence to support this claim is mainly anecdotal, a clinical trial was carried out using an electric pulp tester (EPT) to measure the extent and duration of any analgesic effect induced by pulsed Nd: YAG laser treatment. A double-blind crossover experiment involving laser and sham treatments was used on 21 subjects. A small (3.6 arbitrary units) but statistically significant increase was observed in the mean responses measured 5 min after laser treatment with 113 mJ pulses at 15 pulses s-1 (pps) for 3 min. The pain thresholds returned to baseline values after 60 min. No statistically significant changes in threshold were found with the sham treatment. The order in which laser and sham treatment was received made no difference to the results.

Application of Transverse Microradiography for Measurement of Mineral Loss by Acid Erosion

This paper describes a novel application of transverse microradiography for the detection and quantification of mineral loss due to acid erosion in thin tooth sections. Sixty-four specimens were randomly divided into eight equal-sized groups and exposed to an orthophosphoric-acid-based erosive fluid (pH = 3) for 0, 0.25, 0.5, 1, 2, 5, 12, or 24 hrs. We made microdensitometric scans separately across both enamel and dentin to derive data for the total mineral loss and the minimum mineral content within the eroded area. We then analyzed specimens using a profilometer to determine (1) the area above a plot of penetration depth against distance and (2) the maximum depth of penetration. Correlation coefficients for comparisons between microradiographic and profilometric data for both enamel and dentin specimens varied between 0.87 and 0.96. Two-sample t tests demonstrated that the microradiographic technique could detect early erosion, i.e., discriminate between erosion times of less than 1 hr. It was concluded that this application of transverse microradiography was a useful and acceptable method for the measurement of early mineral loss in vitro, occurring as a result of acid erosion.

The Effect of Chewing Gum Use on in situ Enamel Lesion Remineralization

Two independent cross-over studies investigated the possibility of enhanced early enamel lesion remineralization with the use of chewing gum. The first study involved a sorbitol-containing chewing gum, and the second, which had an identical protocol, tested a sucrose-containing chewing gum. In each study, 12 volunteers wore in situ appliances on which were mounted enamel sections containing artificial caries lesions. Subjects brushed twice daily for two min with a 1100-ppm-F (NaF) dentifrice (control and test) and in the test phase chewed five sticks of gum per day for 20 min after meals and snacks. Microradiographs of the enamel lesions were made at baseline and at the end of the seven-week experimental period. In the sugar-free gum study, the weighted mean total mineral loss (Az) difference [(wk7 - wk0) x (-1)] was 788 vol.% min. x μm for the gum, corresponding to remineralization of 18.2%, vs. the control value of 526 vol.% min. x μm, 12.1% remineralization (p = 0.07). There were no significant differences for the surface-zone (p = 0.20) and lesion-body (p = 0.28) values. In the sucrose-containing gum study, the Az difference was 743 vol.% min. x μm for the gum, corresponding to a remineralization of 18.3%, vs. the control value of 438 vol.% min. x μm, 10.8% remineralization (p = 0.08). The surface-zone values were not significantly different (p = 0.55). For the lesion body, however, the sucrose-containing gum value of 6.11 vol.% min. was significantly different (p = 0.01) from that of the control (2.81 vol.% min.).

The Effect of Dentine on Fluorescence Measurements of Enamel Lesions in vitro

This study aimed to determine the contribution of the underlying dentine and the enamel-dentine junction to measurements of mineral loss from enamel recorded using quantitative light fluorescence (QLF). Sixteen square blocks (5 × 5 mm) were cut from the labial surfaces of extracted bovine incisor teeth. A dental drill was used to remove dentine and the enamel-dentine junction from half of each specimen. All specimens were embedded in epoxy resin and ground to produce a smooth, flat enamel surface. Half of the enamel surface of the block, perpendicular to where the dentine had been removed, was demineralised for 72 h prior to undertaking QLF measurements from the enamel surface to compare fluorescence loss from different areas of the block. QLF readings taken from lesions with no underlying dentine or enamel-dentine junction were very similar to readings from lesions with underlying dentine. A comparison of the two data sets demonstrated a linear relationship with a gradient of 0.95 and a y intercept of –1.24 (r2 = 0.936). From these data, the underlying dentine and enamel-dentine junction did not influence mineral loss in enamel measured using QLF.

Determination of Plaque pH Changes within the Trough of an in situ Appliance Used to Study Mineral Changes in Early Carious Lesions

Plaque pH was measured using a glass combination pH microelectrode of plaque deposits lining the trough of an intra-oral appliance which contained single sections of human teeth with artificial enamel lesions. Plaque exposure to a 10% sucrose solution produced significantly lower plaque pH levels than a solution of sorbitol gum extract. The subsequent flow of saliva over the plaque/pH electrode interface resulted in a significant and rapid increase in pH. Repeat experiments, using deionised water instead of saliva, demonstrated no increase in pH at the plaque/electrode interface. This system may provide a convenient method of producing plaque suitable for repeated pH analysis in intimate association with artificial enamel lesions. This may permit further study of the relationship between plaque acidogenicity, salivary buffering capacity and mineral change within the incipient enamel lesion.

Application of a novel confocal imaging technique for the early detection of dental decay

In order to stop or prevent the progression of dental disease, early detection and quantification of decay are crucially important. Dental decay (caries) detection methods have traditionally involved clinical examination by eye, using probes and dental radiography, but up to 60% of lesions are missed. What the dentist requires is a cheap, reliable method of detection of early disease, ideally with information on the depth and rate of growth or healing. Conventional commercial scanning confocal microscopes are unsuitable for use on dental patients. We report on a fibre optic based confocal microscope designed for in vivo examination of caries lesions. The system utilizes a common fibre both as the source and to detect the reflected confocal signal. The initial system has been optimized using dielectric mirrors and the thickness of the stack has been measured with high precision. Dental samples have been examined and the system has been demonstrated to provide information on the depth and mineral loss of a lesion. Fibre optic microscopy (FOCM) demonstrates a practical route to developing an in vivo caries profiler. In this paper, the FOCM and its applications in caries detection are described and the potential of this scheme as a practical dental probe is discussed.

Blue-laser-diode-excited fluorescence spectroscopy of natural carious lesions

We report on the use of a blue laser diode to excite natural fluorescence from a range of dental samples. Sixty teeth with naturally occurring lesions were examined. The lesions were classified on visual inspection as falling into three classes as shiny lesions, dull lesions and brown lesions. The resulting fluorescence was then examined using a fibre optically coupled spectrometer in a series of wavelength bands. By examining the intensity ratios in the two wavelength bands 480-500nm and 620 to 640nm we were able to classify the lesion types and thus provide a quantifiable measurement of lesion types. This method has application for detection of dental caries as well as demonstrating potential application to evaluate lesions which may represent different degrees of caries activity.